Tyngsborough (also spelled Tyngsboro) is a town in northern Middlesex County, Massachusetts, United States. Tyngsborough is 28 miles (45 km) from Boston along the Route 3 corridor, and located on the New Hampshire state line. As of the 2010 census, the town population was 11,292.

According to the United States Census Bureau, the town has a total area of 18.0 square miles (47 km2), of which 16.9 square miles (44 km2) is land and 1.2 square miles (3.1 km2) (6.65%) is water. Tyngsborough is bordered by the towns of Dunstable, Groton, Westford, Chelmsford, and Dracut, by the city of Lowell, and by the New Hampshire communities of Hudson, Pelham (though no road connects the two towns directly), and Nashua. Besides a series of lakes and ponds that dot Tyngsborough, the town is split in two by the Merrimack River which runs roughly north-south near the center of town. The land is mostly rolling hills, small cleared fields, and wooded land. Marshlands can also be found in the area, although they are less prevalent than in surrounding towns.

As of the census of 2000, there were 11,081 people, 3,731 households, and 2,947 families residing in the town. The population density was 657.4 people per square mile (253.8/km≤). There were 3,806 housing units at an average density of 225.8 per square mile (87.2/km≤).